1. Field of the Invention
The present invention relates to a charging circuit and an amplifier.
2. Description of the Related Art
A charge pump circuit is known as a circuit that applies a boosted voltage generated by boosting an input voltage to a load, such as a capacitor (see, e.g., Japanese Laid-Open Patent Publication No. 2006-50833). Because the charge pump circuit usually generates the boosted voltage in synchronization with an input clock signal, noises are included in the boosted voltage. To eliminate such noises, for example, an LPF (Low-pass Filter) may be placed between the charge pump circuit and the capacitor as a load.
Capacitive loads driven by the charge pump circuit include, for example, a capacitor for a microphone that detects an audio signal. When the charge pump circuit is used as a power supply circuit, a load, such as an LED, may be connected to the capacitor as a load. For this reason, it is important for the charge pump circuit to boost the charge voltage of the capacitor as the load in a shorter time. When the LPF is provided to eliminate noises included in the boosted voltage, as described above, however, a time needed for boosting the charge voltage of the capacitor gets longer than a time need in a case of not providing the LPF. To deal with this problem, for example, the frequency of a clock signal for operating the charge pump circuit may be increased to shorten the time needed for boosting the charge voltage of the capacitor. This case, however, brings a problem that an increase in the frequency of the clock signal leads to an increase in power consumption by the charge pump circuit.